PV and solar cleaning: Everything you need to know!

PV and solar cleaning : An overview of a major topic!

Hardly anyone doubts that PV and solar systems need to be cleaned. Especially on large and therefore often increasingly flat systems, performance increases of more than 10% can almost always be generated. More and more operators and owners want to clean their systems or even have to do so several times a year due to particularly large amounts of dirt. What is this type of cleaning all about? What should be taken into account? What techniques are available? We will go into this in detail today

But if you're in a particular hurry, you can go straight to the right category in our store here: Solar cleaning.

Overview and content on the topic of photovoltaic cleaning:

1. why and how often do PV systems need to be cleaned and what are the benefits?

2. what is the basic approach to cleaning PV and solar systems?

3. which water systems are available for PV cleaning?

4. which brush and cleaning systems are available for photovoltaic systems?

5 How fast can I clean PV systems?

6 How do I deal with problem cases such as lichens and the like?

7. can I use chemicals for PV cleaning and do I even have to?

8 How often should the PV modules be cleaned and how can I calculate the yield loss?

1. why and how often do PV systems need to be cleaned and what are the benefits?

Photovoltaic systems (PV systems) are exposed to the weather and can lose efficiency due to various sources of soiling. Especially systems that are flatter (e.g. less than 30° inclination) tend to build up a film of dirt. Although this is also possible with steeper systems, it happens less quickly and to a lesser extent. Put simply, this film of dirt ensures that the incident light can no longer reach the panels or cells as well, which means that less electricity is produced than would be the case with a clean panel. However, there are also technical and substantial arguments in favor of regular cleaning of the panels. For example, lichens can even migrate through the glass surface of the panels and contribute to hotspots and damage.

The main reasons for cleaning PV and solar systems can therefore be summarized as follows

✅ Increased performance: soiling can reduce efficiency by 5-30%.
✅ Avoidance of hotspots: Accumulations of dirt can cause localized overheating, which damages the modules in the long term.
✅ Longer service life: Regular cleaning can improve the durability of PV modules and keeps the surface of the modules intact.
✅ Better profitability: A clean system produces more electricity and therefore increases profitability.

What types of soiling occur?

Dust and pollen: Especially in agricultural areas or dry regions.
Lichens, leaves and moss: In areas close to forests or with high humidity.
Bird droppings: Can be particularly stubborn and shade parts of the module.
Industrial deposits: Soot, fine dust or chemical residues in urban and industrial areas.
Snow and ice: In winter, a thick layer of snow can completely prevent electricity production. Slipping" or defrosting occurs significantly faster on a clean surface than on a dirty one.
Other exotics: Brake dust from railroad tracks, tree resin, bitumen, deposits after fire damage, starch and grinding dust from agriculture

2 What is the basic approach to cleaning PV and solar systems?

The basic approach to PV and solar cleaning is to wash the surfaces with washing brushes (bristles usually made of nylon) and pure water.
The question of the best medium or solvent for cleaning PV and solar systems follows the trend in glass and façade cleaning. Pure water has various practical advantages here and has become the industry standard over the last 20 years for a number of reasons. Blasting processes (free HD applications, dry ice, sandblasting) are generally out of the question due to the protection of substrates (HD and sandblasting) or high running costs and low surface performance (dry ice).
The use of effective cleaning chemicals is generally out of the question for PV and solar systems, as it is usually impossible or at least uneconomical to collect the dirt. Pure water offers very good cleaning performance, does not have to be collected or is not contaminated and ensures that the surfaces dry without residue, which positively counteracts or delays new soiling.
While the question of the medium or solvent ("pure water") is quite clearly regulated, there is a wide range of options for the selected brushes or brush system. There is a wide variety of options for the brush or brush system selected, which are adapted to the respective design, contamination and size of the systems to be cleaned (fixed brush, rotating brushes, robots, etc.).

3. which water systems are available for PV cleaning?

The principles of "mixed bed resin" or "osmosis technology" are basically used for the treatment of ultrapure water in the field of PV cleaning, as all other processes are too costly or unaffordable.
We have already dealt with the comparison of the two different systems in this article . At the same time, it should be mentioned that the term "osmosis purification" or "osmosis filter" has become established and is now used for all types of pure water systems, which can lead to misunderstandings and errors.

In general, it can be said that real osmosis systems are usually used for cleaning PV modules, as they generate hardly any running costs, which is very important for water-intensive work. And PV cleaning is water-intensive work. Only for "self-cleaning" of smaller systems (e.g. up to max. 100 kWp up to a maximum of 1 cleaning per year), a mixed bed resin may be the right choice.

4 What brush and cleaning systems are available for photovoltaic systems?

We essentially distinguish between three categories of brushes and a special category of "blasting systems for lichen removal" for cleaning PV modules.

These are as follows:

- Rigid, non-rotating, manual hand brushes: For small systems, systems with little soiling or very steep systems.

- Rotating hand brushes (electric or with high-pressure drive): For medium and large installations and higher working speeds (up to 500 kWp, for example).

- Solar robots (self-propelled machines): For large and largest installations (above 500 kWp).

- Lichen remover systems: For basic cleaning of systems with moss and lichen infestation.

Of course, we also offer all of this as part of our popular"complete sets" if required.

5 How fast can I clean PV systems?

Basically, from a PV system size of approx. 50 kWp, we can only start to ask the question of "area per hour" in a meaningful way and really calculate it.
For smaller systems, the issue of "travel time, set-up time and organization" plays such an important role that we have to allow more time for this than for the actual cleaning.
For larger systems, the following has emerged based on 15 years of experience:

- Rigid hand brushes: 50-60 square meters per hour

- Rotating hand brushes: 120-160 square meters per hour

- Solar robots: 400 square meters per hour (small units) / 750 square meters per hour (large units)

- Lichen remover: 25-50 sqm (handheld device) / 125 sqm (robot)

These are all practical "real" performance values that reflect set-up times, travel times, etc. and are calculated from the perspective of a service provider.
All figures also assume normal contamination and do not include special cases (fire damage, tree resin, extreme ranges, floating systems, systems without water and electricity, etc.).

6 How do I deal with problem cases such as lichens and the like if I encounter them on PV modules?

As already described above, we encounter problem cases in PV cleaning from time to time. The most common is certainly the issue of "lichen infestation".
Certified, safe and practical solutions based on vortex jet or rotary nozzles have been available for 2 years, which cut the lichen by means of a fixed entry angle and fixed jet distance, but do not damage the panel or the seals. The topic of "Lichens in PV cleaning" is dealt with separately in this article .

For many special problems, there is no universal solution that works reliably. For example, solar installations close to railroad lines can be left with residues caused by brake dust, which cannot be cleaned properly and are more likely to be classified as damage. Residues from tree resins are similarly problematic in the case of adjacent trees or after fires - especially if they have been in place for a long time. Here, too, it is more a case of damage than contamination that can be removed in an economically viable manner.

In such special cases, we strongly recommend carrying out a work trial with the customer and agreeing a disclaimer regarding the result and surface condition. This allows us to proceed on a case-by-case basis and usually work with textile-based processes or develop an alternative solution. However, it often turns out that there is ultimately damage here too or that the cleaning costs would exceed the replacement with new modules.

For service providers in particular, it is therefore crucial to recognize such cases in advance of cleaning and to clearly differentiate themselves - in case of doubt, even to refrain from making an offer or accepting an order.

7 May I use chemicals for PV cleaning and do I even have to?

We have already dealt with this question in detail in the following article . Basically, it should be noted that there are currently no effective and legally safe cleaning products that can be used without collecting the dirt, particularly in view of the legal requirements in Germany. Regardless of how gentle or high quality a cleaning agent is - this aspect is a central exclusion criterion for the use of chemical agents in solar cleaning and the often quoted "biodegradable" label does not help here either (does not contain any information about the infiltration permit). In practice, the collection of the cleaning solution is usually technically almost impossible or economically unviable - even for roof systems this is necessary as the cleaning solution must not be allowed to enter the roof drainage system.

Although various cleaning agents are freely available on the market, the decisive factor is the information in the respective safety data sheets - and these are legally binding. They regularly state that the agents must not seep into the ground and that the dirt must be collected. In many cases, it is also noted that the collected liquid must not even be discharged into the sewage system.

The use of chemical cleaning agents in the commercial sector is therefore generally impractical. Apart from causing considerable environmental damage, it carries a high liability risk - especially for companies or service providers who use such products outdoors.

8. how often should the PV modules be cleaned and how can I calculate the loss of yield?

Basically, most solar systems need to be cleaned once a year. Especially for small, private PV systems with very steep roofs (over 30° inclination) and low environmental influences, cleaning may only take place after 3-5 years. The fact that "large" systems are very often flatter and also tend to be located in dirt-intensive areas (agriculture, highways, industrial areas) also speaks in favor of cleaning more often than once a year. Our PV loss calculator is a very useful tool for calculating when cleaning is advisable, not only from a material point of view but also from an economic point of view. You can find it here: PV loss calculator.